Filtrering og UV-bestråling - veien fra avløpsvann til vanningsvann

As world water demand grows, its reclamation and reuse becomes increasingly important. It is expected that global demand for water will exceed supply by 40% in 2030. In addition, it is expected that the world population will pass 8.5, 9.7 and 10.9 billion people by the end of 2030, 2050 and 2100 respectively. The aim of this study is to investigate the efficiency of UV-light for wastewater disinfection. The quality of wastewater for reuse purposes, such as irrigation, must be in compliance with EU regulations. One of the main purposes of wastewater disinfection is to ensure permanent inactivation and prevent UV-repair of microorganisms, such as thermotolerant coliform bacteria (TCB) including E. coli. Water quality is one of many factors that affects the performance of UV-disinfection. Suspended solids, which can shield microorganisms from UV-light can reduce the UV-efficiency. Samples from two different wastewater treatment plants was used to determine the UV-performance. Sufficiently high log inactivation was not achieved with the samples of secondary wastewater treatment. However, the implementation of a sand filter before UV-irradiation led to a reduction of suspended solids and turbidity, as well as a significant reduction in TCB concentration in the range of 52-56%. With the sand-filtration as a final purification step before UV-irradiation, a 5-log inactivation target was effectively met with a UV-dose of 20 mJ/cm2. Potential UV-repair can as well be reduced by applying a sufficient UV-dose. Sand-filtration have demonstrated beyond any doubt the improved effectiveness of UV in removal of microorganisms in wastewater